Intracellular osmoregulation by the myocardium of the euryhaline elasmobranch skate, Raja erinacea, will be studied in vivo and in vitro to characterize the membrane transport processes involved in adjusting the intracellular osmolyte content to wide variations in the osmolarity of the extracellular fluid environment. Pharmacogenetics: Dose-response effects and time course events following atrophine administration will be obtained from specially bred rabbit strains that are double recessives (as/as), heterozygous (As/as) or homozygous dominants (As/As) for a circulating enzyme, atropine esterase, whose activity is determined by the genetic input. Cardiac output, arterial blood pressure, total peripheral resistance and the major parameters of renal hemodynamics will be evaluated. Active transport by renal proximal tubule cells in tissue culture will be studied with the objective of relating onset of secretory activity in cells undergoing maturation to alterations in cellular fine structure that simultaneously take place. BIBLIOGRAPHIC REFERENCES: Forster, R.P. My forty years at the Mount Desert Island Biological Laboratory. J. Exper. Zool.198: #6 (March), 1977, in press. Boyd, T. A., Chung-Ja Cha, R. P. Forster and L. Goldstein. Free amino acids in tissues of the skate Raja erinacea. J. Exper. Zool. 198: #6 (March), 1977, in press.